<template>
  <ul class="list">
    <li class="item" 
      v-for="item of letters" 
      :key="item"
      @click="handleLetterClick"
      :ref="item"
      @touchstart.prevent = "handleTouchStart"
      @touchmove = "handleTouchMove"
      @touchend = "handleTouchEnd"
      >{{item}}</li>
  </ul>
</template>
<script>
import Bscroll from 'better-scroll' 
export default {
  name: 'CityAlphabet',
  props:{
    cities: Object
  },
  data(){
    return {
      status : false,
      offTop : 0,
      timer : null
    }
  },
  updated(){
    this.offTop = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters(){
      const letters = []
      for( let i in this.cities ){
        letters.push( i )
      }
      return letters
    }
  },
  methods:{
    handleLetterClick(e){
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart(){
      this.status = true
    },
    handleTouchMove(e){
      if(this.status){
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer = setTimeout( ()=> {
          const clientTop = e.touches[0].clientY - 79
          const index = Math.floor( (clientTop - this.offTop) / 20 )
          if( index >= 0 && index < this.letters.length ){
            this.$emit('change',this.letters[index])
          }
        } ,8)
      }
    },
    handleTouchEnd(){
      this.status = false
    }
  }
}
</script>
<style lang='stylus' scoped >
  @import '~styles/varibles.styl'
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    .item 
      line-height .4rem
      text-align center
      color $bgColor

</style>
